A substantial share of manufactured polymers are used as packaging for consumer products, such as personal care product packages (e.g., shampoo, conditioner, and soap bottles) and fabric and household care product packages (e.g., for laundry detergent and cleaning compositions). Most of the materials used to produce polymers for plastic packaging applications, such as polyethylene, polyethylene terephthalate, and polypropylene, are derived from monomers (e.g., ethylene, propylene, terephthalic acid, ethylene glycol). These monomers are typically obtained from non-renewable, fossil-based resources, such as petroleum, natural gas, and coal. The price and availability of these resources significantly influence the price of polymers used for plastic packaging. As the availability of these resources diminishes, monomer prices increase, and so too does the price of products (e.g. polymers) made from these resources. There is therefore a continuing need to recycle these polymers for use or re-use in these same applications. Heretofore, however, the art has encountered difficulties in processing recycled plastics for further use in injection molding.
Bertrin et al. (2002) Euro Polym Jnl 38:2255-64 suggested the use of various compatibilizing agents where the recycled materials are blends of low density polyethylene and polypropylene. For example, the impact strength of these blends have been improved with the addition of compatibilizing agents, such as ethylene diene monomers, ethylene propylene monomers, or PE-g-(2-methy)-1,3-butadiene) graft copolymers.
In a patent application filed in 2003, Suzuki described a process for injection molding a composition that includes recycled thermoplastic resin and one recycle aid agent that tempers or prevents degradation of the mechanical properties of the recycled resin. See U.S. patent publication No. 2005/0127579 A1. The recycled resin includes, among others, olefin resins such as polyethylene, polypropylene, and copolymers of ethylene and propylene. The recycle aid agent includes, among others, rubber-like materials that include an olefin group rubber as a “trunk” portion of the material and, as a branch part of the material, a graft chain compatible with the recycled resin. The olefin group rubber can be a copolymer of ethylene and an α-olefin, such as ethylene-propylene copolymer rubber (EPM), ethylene-propylene-non-conjugated diene compound terpolymer (EPDM), ethylene-butene copolymer rubber (EBM), and ethylene-butene-non-conjugated diene compound terpolymer (EBDM). Whatever the recycle agent, Suzuki teaches that it may be added to the plastic resin in an amount of about 1 weight percent (wt. %) to about 10 wt. %, and the resulting mixture then injection molded. Furthermore, Suzuki teaches the need to combine recycling aids with more complex and more expensive gas assist and expansion injection molding methods to achieve any improvements in mechanical properties.
In 2005, Chang et al. described a combination of a propylene-based elastomer and a homogeneous ethylene-alpha olefin interpolymer, present in a weight ratio of 97:3 to 80:20, that can be used with another propylene-based polymer (such as homopolymer polypropylene, random copolymer polypropylene, and/or impact copolymer) to improve physical properties of the polymer. See U.S. Pat. No. 7,893,161 B2.
In 2008, Brachet et al. recognized the difficulty in maintaining a constant quality of recycled materials and that up to 10% of foreign materials can be found in recycled polypropylene even if well sorted. They posited that the mechanical properties of recycled polypropylene from post-consumer containers could be improved with the addition of calcium carbonate and ethylene-octene rubber (such as ENGAGE 801 available from the Dow Chemical Company (Midland, Mich.), which is a copolymer of the alpha-olefin octane and ethylene). But they reported that the results of their tests did not show an improvement because of the presence of a crystalline fraction of polyethylene that contaminated the recycled polypropylene.